Umm, Make certain your actually using the throttle... Sounds like a smart assed answer but unconciously you are prolly holding back. The front should loft really easy with the "snap into the throttle" technic. Take your time and be certain your using your throttle effectively. That front should climb straight up at just about any RPM in First... I mean I can pop it up in parking lots at about 30mph, and I can bring it up at 5500 rpms in first with a quick snap...
It might have something to do with your rear tire slipping, maybe altitude... but more than likely, you just not twisting it like you think you are...
Not trying to be a bobo, I am not a Fugging wheelie expert, but getting that front to come off the ground is really easy. Riding that front out is something different altogether. But hell, If you just tuck in from a start and roll that throttle to the stop the front should come up all on it's own at about 6-7K or so, no input required from you... No 12 O'clocks, but fun little wheelies...